Two-photon absorption and excited-state refractions in anthraquinone dyes

We examine the nonlinear optical properties of solutions of 9,10-anthraquinone, 1,4-dihydroxy-anthraquinone, 5,8-dichloro-1,4-dihydroxy-anthraquinone and 1,4-bisethyl amino-anthraquinone by means of the intensity-dependent transmission and the Z-scan method with 532 nm 8 ns pulses. The results demonstrated that the 9,10-anthraquinone displayed a two-photon absorption (TPA) character. The molecular TPA cross section of this compound is estimated as sigma(2) = 7.22 x 10(-19) cm(4)/GW or sigma(2) = 26.96 x 10(-48) cm(4)/photon/s, respectively, and an essential state of 'm(1)A(g)', which should be located near the 2 omega virtual transition state, is predicted. On the other hand, the effective excited-state nonlinear refractive coefficients n(2)(eff) these anthraquinones are found to be similar to 10(-10) esu, which are comparable with those highly conjugated planar molecules of tetrabenzporphyrins and phthalocyanines.